1. Field of the Invention
The present invention relates to a high speed uniformity measurement device for a tire. In particular, the present invention relates to a high speed uniformity measurement device for a tire, in which a high speed uniformity of a tire which is conveyed on a production line can be automatically and continuously measured.
2. Description of the Related Art
High speed uniformity, which is a basic characteristic of a product tire, is used for verification of matching data for a vehicle body (suspension) and a tire at a tire manufacturer and an automobile manufacturer.
High speed uniformity is measured by a conventional high speed uniformity measurement device in the following manner: a tire to be measured is mounted on a rim which is being commercially sold, the tire inflated with air is set on a sensor which is on a spindle axis manually by an operator, the tire is pressed by a load drum, and the load drum is rotated at a high speed in a state in which a constant load is applied to the tire.
However, in the conventional high speed uniformity measurement device, it takes time to mount the tire on the rim, inflate the tire with air and set the tire on the measurement device in order to measure the uniformity. Also, it takes time to remove the tire which is set on the measurement device after the measurement is completed. Moreover, it costs much to operate the measurement device, because the operations, for example, mounting the tire on the rim, setting the tire on and removing the tire from the measurement device, running the measurement device and collecting data, are performed manually by the operator. Further, because an internal pressure of the tire changes when the tire is rotated, a long warm up time for the internal pressure of the tire to stabilize is necessary in order to start the measurement.
Accordingly, in the conventional high speed uniformity device, it is very difficult to continuously and automatically measure the high speed uniformity of a tire which is conveyed on a production line.
Moreover, the first order factor of the high speed uniformity is influenced by residual unbalance. Accordingly, not only the high speed uniformity, but also the residual unbalance is measured, and it is necessary that data, in which a measured value of the residual unbalance is removed from a measured value of the high speed uniformity, is evaluated. There are two methods of measurement of the residual unbalance. One method is such that the tire, rotating at a speed which is equal to or more than a target speed, is made to rotate inertially in a non-load condition, and the measurement is performed. The other method is such that a high speed TFV (tangential force variation) of a target speed of the tire is measured in a skim-touch condition (in a condition in which a load, which is applied to the tire when the tire slightly contacts the ground, is applied), and this high speed TFV is used as a substitute value for the residual unbalance. Therefore, it is necessary that, after the high speed uniformity is measured, the tire is rotated again at a high speed in a state in which a load by the load drum is not applied to the tire, the residual unbalance is measured, and data of the results of the measurement of the high speed uniformity is corrected manually. Accordingly, there is the problem that time and costs are required.
On the other hand, a low speed uniformity measurement device has an automatic detachable mechanism by a half rim, and a variation component of the load (a vertical force) of the tire xe2x80x9cRFV (radial force variation)xe2x80x9d and a variation component of the lateral force of the tire xe2x80x9cLFV (lateral force variation)xe2x80x9d are measured by a sensor attached to a load drum axis.
One may think that high speed uniformity could be automatically continuously measured by use of the automatic detachable mechanism by the half rim. However, a variation component of a fore-and-aft load of the tire xe2x80x9cTFV (tangential force variation)xe2x80x9d cannot be measured by a low speed uniformity measurement device because the sensor is attached to the load drum axis. Also, because the low speed uniformity is not influenced by residual unbalance, a mechanism for measuring residual unbalance is not provided at the low speed uniformity measurement device.
Furthermore, when high speed uniformity is measured by the conventional high speed uniformity measurement device, a long time is required for the following reason. In a tire rotating speed increasing period which includes a time from when the tire is not rotated until a rotation speed of the tire reaches a target rotating speed, and in a tire rotating speed decreasing period which includes a time from when the tire rotates at the target rotation speed until the rotation of the tire is stopped, measurement is not performed. Measurement is performed in a state in which the rotation speed of the tire is maintained at a constant high rotation speed.
The present invention takes the facts mentioned above into consideration, and an object of the present invention is to provide high speed uniformity measurement device for a tire, in which a high speed uniformity of a tire conveyed on a production line can be automatically and continuously measured.
Another object of the present invention is to provide a high speed uniformity measurement device for a tire, in which the high speed uniformity can be measured in a short time.
In order to achieve the object mentioned above, in accordance with a first aspect of the present invention, there is provided a high speed uniformity measurement device comprising: a pair of rim shafts, one rim shaft of the pair of rim shafts being able to be disposed above and another rim shaft of the pair of rim shafts being able to be disposed below a conveyor which conveys a tire such that the pair of rim shafts sandwiches the conveyor, and each rim shaft of the pair of rim shafts is provided with a half rim for sandwiching the tire, and the pair of rim shafts sandwich or release sandwiching of the tire being conveyed on the conveyor; a load drum which is movable in directions of approaching and moving away from the tire, the load drum applying a load to the tire which is sandwiched between the half rims, while the load drum is pushed against the tire and rotates together with the tire; an air filling and releasing portion for filling the tire sandwiched between the half rims with air, and for releasing air from the tire; and a high speed uniformity measuring portion which measures high speed uniformity in a state in which load is applied to the tire which is filled with air and the rotational speed of the tire is varied.
In accordance with the first aspect of the present invention, a pair of rim shafts are disposed above and beneath a conveyor which conveys a tire, so as to sandwich the conveyor. A half rim is provided at each rim shaft. By using the half rims, the pair of rim shafts sandwich the tire which is being conveyed by the conveyor, and release the tire after measurement has been completed, and the tire is put again on the conveyor. A load is applied to the tire which is being sandwiched by the half rim, by a load drum which moves in directions of approaching and moving away from the tire. Further, an air filling and releasing portion fills the tire sandwiched between the half rims with air (inflates the tire with air), and releases the air filled in the tire after measurement has been completed. Then, at the high speed uniformity measuring portion, the high speed uniformity is measured in a state in which load is applied to the tire filled with air and the rotational speed of the tire is varied.
In the first aspect, a mechanism for automatically attaching and releasing the tire by the half rims is provided. Thus, the tire which is being conveyed can be automatically attached and released, and the time required for attaching and releasing the tire for measurement thereof can be reduced. Moreover, because the filling of the tire with compressed air and the releasing of the compressed air from the tire can carried out automatically, the time for measurement can be shortened.
A second aspect of the present invention is a high speed uniformity measurement device according to the first aspect, wherein the high speed uniformity measuring portion measures high speed uniformity in a state in which load is applied to the tire and the rotational speed of the tire is varied in a first direction, and the high speed uniformity measuring portion measures residual unbalance in one of a state in which load is not applied to the tire and the rotational speed of the tire is varied in a second direction which is different than the first direction, or a state in which the load is applied to the tire right before the tire contacts ground, and the rotational speed of the tire is varied in the second direction, and a first order component of high speed uniformity is determined on the basis of subtracting a measured value of residual unbalance from a measured value of high speed uniformity.
In the second aspect, the high speed uniformity is measured in a state in which load is applied to the tire which is filled with air and the rotational speed of the tire is varied in a first direction (the raising direction or the lowering direction). The first order component of the high speed uniformity is affected by the residual unbalance. Thus, separately from the high speed uniformity, the residual unbalance is measured in one of the following two states: (1) a state in which no load is applied to the tire and the rotational speed of the tire is varied in a second direction (the lowering direction if the first direction is the raising (increasing) direction, or the raising direction if the first direction is the lowering direction), or (2) a state in which a load is applied to the tire, which load is equal to the load which is applied to the tire immediately before the tire contacts the ground, and the rotational speed of the tire is varied in the second direction. Then, by subtracting the measured value of the residual unbalance from the measured value of the high speed uniformity, the first order component of the high speed uniformity is determined.
In a case in which the first order component of the high speed uniformity is determined, when an attempt is made to measure the high speed uniformity and the residual unbalance within one cycle in which the tire rotational speed is raised and then lowered, a measurement timing cannot be achieved. Therefore, the high speed uniformity and the residual unbalance at a predetermined rotational speed within a measurement speed range are measured.
Further, given that the unbalance m on the tire circumference rotates at a tire rolling radius r and an angular speed xcfx89, the residual unbalance can generally be expressed as mrxcfx892. The relationship between the rotational speed of the tire and the residual unbalance can substantially be expressed as a second order regression curve. Here, based on the high speed uniformity at an arbitrary rotational speed, the residual unbalance corresponding to this arbitrary rotational speed is estimated from the second order regression curve. The residual unbalance corresponding to the arbitrary rotational speed is vector subtracted from the high speed uniformity of the arbitrary rotational speed. Accordingly, a first order component of the high speed uniformity which has been corrected by the residual unbalance can be determined.
In the second aspect of the present invention, the high speed uniformity of the tire is measured in a state in which the rotational speed of the tire is varied in a first direction, and the residual unbalance is measured in a state in which the rotational speed of the tire is varied in a second direction. Therefore, the high speed uniformity and the residual unbalance can be measured within the period of time in which the tire rotates from the stopped state and then again returns to the stopped state. There is no need to maintain the rotational speed of the tire constant each time a predetermined rotational speed is reached. Thus, the first order component of the high speed uniformity of the tire can be determined in a short time.
A third aspect of the present invention is a high speed uniformity measurement device according to the first aspect, wherein the high speed uniformity measuring portion is provided at a position other than at the load drum.
A fourth aspect of the present invention is a high speed uniformity measurement device according to the third aspect, wherein the high speed uniformity measuring portion is provided at the pair of rim shafts.
A fifth aspect of the present invention is a high speed uniformity measurement device according to the second aspect, wherein the high speed uniformity measuring portion determines the first order component of the high speed uniformity by determining a relationship between a rotational speed of the tire and residual unbalance, and subtracting, from the measured value of the high speed uniformity at a predetermined tire rotational speed, a residual unbalance at the predetermined tire rotational speed which residual unbalance is estimated on the basis of the relationship.
A sixth aspect of the present invention is a high speed uniformity measurement device according to the first aspect, wherein the high speed uniformity measuring portion measures high speed uniformity in a state in which load is applied to the tire and the rotational speed of the tire is varied, and at least one of high order components of the high speed uniformity is determined.